Method of preparing aluminum alloy resin composite and aluminum alloy-resin composite obtainable by the same

ABSTRACT

A method of preparing aluminum alloy-resin composite and an aluminum alloy-resin composite obtained by the same are provided. of the method comprises: S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, the oxide layer including nanopores; S2: immersing the resulting aluminum alloy substrate obtained in step S1 in a buffer solution having a pH of about 10 to about 13, to form a corrosion pores on an outer surface of the oxide layer; and S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained in step S2 in a mold to obtain the aluminum alloy-resin composite.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent Application No. PCT/CN2012/082031, filed Sep. 26, 2012, which claims priority to and benefits of Chinese Patent Application Serial No. 201210043640.1, filed with the State Intellectual Property Office of P. R. China on Feb. 24, 2012. The entire content of the above applications is incorporated herein by reference.

FIELD

The present disclosure relates to the field of metal-plastic molding, and more particularly to a method of preparing aluminum alloy-resin composite and an aluminum alloy-resin composite obtained by the same.

BACKGROUND

In manufacturing articles, such as automobiles, household appliances and industrial machines, a metal and a resin often need to be firmly bonded together. In conventional methods, an adhesive may be used at normal temperature or under heating to integrally bond a metal and a synthetic resin. Alternatively, a resin may be bonded to a magnesium alloy, an aluminum alloy, or ferroalloys such as stainless steel directly without an adhesive.

Nano molding technology (NMT) is a technique of integrally bonding a metal and a resin, and allows the resin to be directly injection molded on a surface of a metal sheet by nano molding the surface of the metal sheet so as to obtain a metal-resin integrally molded product. For effective bonding of a metal and a resin, NMT may replace commonly used insert molding or zinc-aluminum or magnesium-aluminum die casting so as to provide a metal-resin integrally molded product with low cost and high performance. Compared with other bonding technologies, NMT may reduce the weight of the final product, may ensure excellent strength of the mechanical structure, high processing rate, high output, and allows more appearance decoration methods, consequently applicable to vehicles, IT equipment, and 3C products.

SUMMARY

Embodiments of the present disclosure solve at least one of the problems existing in the prior art and, particularly, technical problems of weak combination force between the aluminum alloy and the resin in an aluminum alloy-resin composite. And the present disclosure provides a method of preparing an aluminum alloy-resin composite with strong combination force between the aluminum alloy and the resin, thereby facilitating mass production and reducing pollution.

According to a first aspect of the present disclosure, there is provided a method of preparing an aluminum alloy-resin composite structure, comprising:

S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, in which the oxide layer is formed with nanopores;

S2: immersing the resulting aluminum alloy substrate obtained at step S1 in a buffer solution having a pH of about 10 to about 13, to form corrosion pores in an outer surface of the oxide layer;

S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained at step S2 in a mold to obtain the aluminum alloy-resin composite.

According to a second aspect of the present disclosure, there is provided an aluminum alloy-resin composite structure, obtained by the method according to the first aspect of the present disclosure.

A unique two-layer spatial pore structure may be formed on the surface of aluminum alloy, by means of the method according to embodiments of the present disclosure. An aluminum oxide layer may be formed on the surface of the aluminum alloy, and the aluminum oxide layer includes nanopores with desired properties. According to embodiments of the present disclosure, the nanopores having an average diameter of about 10 to about 100 nm may be formed, which has a unique structure and has well connectivity with the resin.

By means of further corrosion, corrosion pores may be formed on the outer surface of the aluminum oxide layer and to be contacted with the resin. The corrosion pores may have a larger diameter than nanopores. According to embodiments of present disclosure, the nanopores having an average diameter of about 200 nm to about 2000 nm may be formed on the outer surface, which have a unique structure and contribute to enhance the connectivity of the resin with the aluminum alloy.

At the following molding step, the resin may penetrate into the pores in the inner layer through the relative bigger pores on the outer surface of the aluminum alloy, thereby making the molding easier compared with prior art. According to embodiments of the present disclosure, the aluminum alloy may be joined to the resin tightly without additional bonding, while providing a higher strength. According to embodiments of the present disclosure, is the method has little influence on the size of metal substrate and the appearance of the aluminum alloy, and generates relatively less heat in the course of processing. Meanwhile, the resin may be easily injection molded into the corrosion pores with larger diameter on the surface, and there is no particular requirement on the resin. The present technical solution may be used widely, is environment-friendly, and may be adopted for mass production.

Additional aspects and advantages of embodiments of present disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the disclosure will become apparent and more readily appreciated from the following descriptions taken in conjunction with the drawings in which:

FIG. 1 shows a two-layer spatial pore structure in the aluminum oxide layer prepared in one embodiment of the present disclosure;

FIG. 2 shows a scanning electron microscopy diagram of an aluminum alloy sheet surface after surface treatment 1 in Example 1; and

FIGS. 3a and 3b show scanning electron microscopy diagrams of the aluminum alloy sheet surface after surface treatment 2 in Example 1.

DETAILED DESCRIPTION

Reference will be made in details to embodiments of the present disclosure. The embodiments described herein are explanatory, illustrative, and used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure.

According to a first aspect of the present disclosure, a method of preparing an aluminum alloy-resin composite is provided. The method comprises steps of:

S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, in which the oxide layer, namely a layer of aluminum oxide film, is formed with nanopores.

According to embodiments of the present disclosure, at this step, aluminum alloy substrate, optionally pre-treated prior to step S1, may be subjected to anodization treatment. Thus an oxide layer may be formed on the surface of the aluminum alloy substrate, with nanopores. According to embodiments of the present disclosure, the method for the anodization treatment is known to the skilled person in the art.

According to embodiments of the present disclosure, at the step S1, namely the anodization treatment, may comprise: providing an aluminum alloy substrate, optionally pre-treated prior to this step, as an anode in a H₂SO₄ solution with a concentration of about 10 wt % to about 30 wt %; and electrolyzing the aluminum alloy substrate at a temperature of about 10° C. to about 30° C. at a voltage of about 10V to about 20V for about 1 minute to about 40 minutes to form the oxide layer with a thickness of about 1 μm to about 10 μm on the surface of the aluminum alloy substrate. According to embodiments of present disclosure, any apparatus well known for the anodization treatment may be applied in the present disclosure. For example, according to an embodiment of the present disclosure, an anodization tank may be applied.

According to embodiments of the present disclosure, the oxide layer formed by means of anodization treatment may have a preferred thickness of about 1 μm to about 5 μm. According to embodiments of the present disclosure, the nanopores of the oxide layer may have an average diameter of about 10 nm to about 100 nm. According to embodiments of the present disclosure, the nanopores of the oxide layer may have an average diameter of about 20 nm to about 80 nm. According to embodiments of the present disclosure, the nanopores of the oxide layer may have an average diameter of about 20 nm to about 60 nm. According to embodiments of the present disclosure, the nanopores may have a depth of about 1 μm to about 5 μm. The nanopores provide improved connectivity force between the oxide layer and the resin.

S2: immersing the resulting aluminum alloy substrate obtained at step S1 in a buffer solution having a pH of about 10 to about 13, to form corrosion pores in an outer surface of the oxide layer.

According to embodiments of the present disclosure, at this step, the resulting aluminum alloy substrate obtained at step S1 may be immersed in a buffer solution with a pH of about 10 to about 13. Thus corrosion pores may be formed on the outer surface of the oxide layer formed on the aluminum alloy substrate. The size of the corrosion pores is usually larger than that of the nanopores. The type of the buffer solution is not limited. According to embodiments of the present disclosure, the buffer solution may comprise a soluble alkali and a soluble dihydrogen phosphate. According to embodiments of the present disclosure, the soluble alkali may be strong alkali.

According to embodiments of the present disclosure, the corrosion pores may have an average diameter of micrometer level. According to embodiments of the present disclosure, the corrosion pores may have an average diameter of up to about 200 nm to about 2000 nm. According to embodiments of the present disclosure, the corrosion pores may have an average diameter of up to about 600 nm to about 2000 nm. According to embodiments of present disclosure, the corrosion pores may have a depth of up to about 0.5 μm to about 9.5 μm. The corrosion pores are communicated with the nanopores. Then, with the forming of corrosion pores, at the subsequent step S3, namely the step of molding, the resin will enter into the pores on the surface of the aluminum alloy substrate in the course of injection molding. Thus the resin layer will be well joined with the aluminum alloy substrate.

According to an embodiment of the present disclosure, the dihydrogen phosphate includes at least one selected from a group including sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, and aluminum dihydrogen phosphate, and the soluble alkali includes at least one selected from a group consisting of sodium hydroxide and potassium hydroxide. Then, with the preferred combination of dihydrogen phosphate and alkali, the corrosion pores are distributed evenly on the surface of oxide layer with uniform diameters, and the pore structure may provide an improved connectivity performance between the resin layer and the aluminum alloy substrate, resulting in a better tensile strength and a better integral joining of the aluminum alloy-resin composite.

According to an embodiment of the present disclosure, the dihydrogen phosphate has a concentration of about 50 wt % to about 99 wt %, and the soluble alkali has a concentration of about 1 wt % to about 50 wt %. According to an embodiment of the present disclosure, the dihydrogen phosphate has a concentration of about 60 wt % to about 99 wt %, and the soluble alkali has a concentration of about 1 wt % to about 40 wt %.

According to an embodiment of present disclosure, step S2 comprises repeatedly immersing the resulting aluminum alloy obtained at step S1 in a buffer solution having a pH of about 10 to about 13 for a plurality of times, such as about 2 to about 10 times, with each immersing lasting for about 1 minute to about 60 minutes. The aluminum alloy is cleaned with water after each immersing by, for example, washing with de-ionized water. According to an embodiment of the present disclosure, the cleaning may comprise placing the article to be cleaned in a washing tank and stand for about 1 minute to 5 minutes or washing the article to be cleaned in a washing tank for about 1 minute to 5 minutes.

S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained at step S2 in a mold to obtain the aluminum alloy-resin composite.

According to embodiments of the present disclosure, at this step, the resulting aluminum alloy substrate after the treatments at steps S1 and S2 may be placed in a mold, and a resin composition may be injected into the mold to be combined with the aluminum alloy substrate. Thus an aluminum alloy-resin composite is formed after the molding treatment.

As mentioned before, prior to the treatment of step S1, the aluminum alloy substrate may be subjected to a pretreatment, which comprises mechanical burnishing or mechanical lapping to remove visible foreign matters from the surface, and degreasing and washing the aluminum alloy substrate to remove processing oil adhered to the metal surface. The pretreatment may comprise burnishing the surface of the aluminum alloy substrate by using, for example, a sand paper of about 100 mesh to about 400 mesh or using a polishing machine, to create small pores of microns. According to embodiments of the present disclosure, the burnished aluminum alloy substrate may be sequentially subjected to oil removing, a first washing with water, alkali etching, a second washing with water, neutralizing, and a third washing with water.

According to embodiments of present disclosure, the aluminum alloy substrate may be cleaned by means of ultrasonic wave using any well-known solvent for about 0.5 hour to about 2 hours to remove oily dirty from the surface of the aluminum alloy substrate, then placed in an acid/alkali aqueous solution, and washed again under ultrasonic wave. The types of the solvents and acid/alkali aqueous solution are not limited, the solvent used may be ethanol or acetone, and the acid/alkali aqueous solution may be at least one selected from a group including hydrochloric acid, sulphuric acid, sodium hydroxide, potassium hydroxide and the like. According to embodiments of the present disclosure, the aluminum alloy substrate is subjected to oil removal treatment using water-free ethanol to remove oil from the surface, and then washed using water. Then, the washed aluminum alloy substrate is immersed in a sodium hydroxide solution at a concentration of about 40 g/L and at a temperature of about 40° C. to about 80° C. to alkali etch the aluminum alloy substrate for about 1-5 minutes, and washed using deionized water. Then, the aluminum alloy substrate is neutralized using a 10-30 wt % HNO₃ to remove trace alkali solution, and washed using deionized water. Thus, a pore with a size of microns may be formed on the surface of the aluminum alloy substrate. According to embodiments of the present disclosure, the diameter of the pore may be about 1-10 μm.

There are no special limitations to the aluminum alloy used in the present disclosure. The aluminum alloy may be Industry-Standard 1000-7000 series, or various aluminum alloys suitable for molding. The aluminum alloy in this disclosure may be commonly-used aluminum alloy with various shapes and structures, which is not limited by the present disclosure. The various shapes and structures of the aluminum alloy may be achieved by mechanical processing.

There is no special limitation to the resin used in the present disclosure, which may be any resin capable of joining with aluminum alloy. In an embodiment, the resin may be a thermoplastic resin. According to embodiments of the present disclosure, the thermoplastic resin includes a mixture of a main resin and a polyolefin resin. According to embodiments of the present disclosure, the main resin may include a non-crystalline resin, which has a surface gloss and a toughness both superior to those of the highly crystalline resins in the prior art. The main resin may be used as an injection molding material. The polyolefin resin with a melting point of about 65° C. to about 105° C. may also be used. Therefore, injection molding at a specific mould temperature may not be required during the molding. Subsequent annealing treatment may also not be required. The molding process may be simplified. It may be ensured that the obtained metal-resin composite has a high mechanical strength and good surface treatment characteristics, thus solving the problem of surface decoration of a plastic article in the prior art and meeting the diverse requirements of customers.

According to embodiments of the present disclosure, it has been found by the inventors through many experiments that, by using a polyolefin resin with a melting point of about 65° C. to about 105° C. in the non-crystalline main resin, the flowing capability of the resin in the nanoscale micropore (i.e., the nanopore) on the surface of the metal sheet may be enhanced, thus ensuring strong adhesive force between the metal and the plastic as well as high mechanical strength of the metal-resin composite structure. Preferably, based on 100 weight parts of the thermoplastic resin, the amount of the main resin is about 70 weight parts to about 95 weight parts, and the amount of the polyolefin resin is about 5 weight parts to about 30 weight parts.

It has also been found by the inventors that the flowing capability of the resin may be enhanced by using a flow improver in the thermoplastic resin, thus further enhancing the adhesive force between the metal and the plastic as well as the injection molding performance of the resin. Preferably, based on 100 weight parts of the thermoplastic resin, the thermoplastic resin further contains about 1 weight part to about 5 weight parts of a flow improver. Preferably, the flow improver is a cyclic polycarbonate.

As mentioned before, the resin used in the present disclosure may be a non-crystalline resin. According to embodiments of the present disclosure, the main resin includes a mixture of polyphenylene ether (PPO) and polyphenylene sulfide (PPS). According to one embodiment of the present disclosure, in the main resin, the weight ratio of polyphenylene ether to polyphenylene sulfide is about 3:1 to about 1:3. According to one embodiment of the present disclosure, in the main resin, the weight ratio of polyphenylene ether to polyphenylene sulfide is about 2:1 to about 1:1. According to embodiments of the present disclosure, the main resin includes a mixture of polyphenylene oxide and a polyamide. According to one embodiment of the present disclosure, in the main resin, the weight ratio of polyphenylene oxide to the polyamide is about 3:1 to about 1:3. According to one embodiment of the present disclosure, in the main resin, the weight ratio of polyphenylene oxide to the polyamide is about 2:1 to about 1:1. According to embodiments of the present disclosure, the main resin includes a polycarbonate, which may be linear chain polycarbonate or branched polycarbonate.

According to embodiments of the present disclosure, the polyolefin resin has a melting point of about 65° C. to about 105° C. The polyolefin resin may be grafted polyethylene. A grafted polyethylene with a melting point of about 100° C. to about 105° C. may be used as the polyolefin resin.

The resin used in the present disclosure may further comprise other modifier additives, and there is no special limitation to the additives. For example, the resin may comprise a filler. And there is no special limitation to the filler. The non-limiting example of the filler is a fiber filler or a powder inorganic filler. The fiber filler may be at least one selected from a group including fiberglass, carbon fiber and aromatic polyamide fiber. And the powder inorganic filler may be at least one selected from a group including calcium carbonate, magnesium carbonate, silica, heavy barium sulfate, talcum powder, glass and clay. According to embodiments of the present disclosure, based on 100 weight parts of the main resin, the content of the fiber filler is 50-150 weight parts and the content of the powder inorganic filler is 50-150 weight parts. The resin has a linear expansion coefficient similar to the aluminum alloy both in horizontal and vertical directions.

According to embodiments of present disclosure, the resin used in the present disclosure may be prepared by mixing the main resin and the polyolefin resin. For example, the resin is prepared by mixing evenly the main resin and the polyolefin resin, and then granulated with a twin-screw extruding machine.

According to embodiments of the present disclosure, a flow improver and a filler may be added to the main resin and mixed evenly. The obtained resin has a linear expansion coefficient similar to the aluminum alloy both in horizontal and vertical directions.

According to embodiments of the present disclosure, the conditions to carry out the injection molding are not limited. For example, according to one embodiment of the present disclosure, the condition of injection molding may be: mold temperature 50 to 300° C., nozzle temperature 200-450° C., pressure maintaining time 1-50 s, injection pressure 50-300 MPa, delay time 1-30 s, cooling time 1-60 s. The amount of injected resin composite is 1-100 g. The surface of the prepared composite has a resin layer with a depth of 0.5-10 μm.

The preparation method of the present disclosure is simple, which significantly simplifies the production process, shortens the production time, and significantly reduces the process complexity, compared with existing techniques. These benefits may be provided by directly injection molding after using the process method of the present disclosure. At the same time, the prepared aluminum alloy-resin composite of the present disclosure provides an improved bonding between the resin layer and the aluminum alloy substrate, and has better tensile shear strength.

According to another aspect of the present disclosure, an aluminum alloy-resin composite may be obtained by the method disclosed herein. According to embodiments of the present disclosure, the aluminum alloy-resin composite comprises an aluminum alloy substrate and a resin layer, in which a resin forming the resin layer is filled in nanopores and corrosion pores. The resin is known resin that can be combined with an aluminum alloy in the art.

The present disclosure will be further described below in detail with reference to examples thereof. It would be appreciated that particular examples described herein are merely used to understand the present disclosure. The examples shall not be construed to limit the present disclosure. The raw materials used in the examples and the comparative examples are all commercially available, without special limits.

Example 1

In this example, an aluminum alloy resin composite was prepared.

1. Pretreatment:

A commercially available A5052 aluminum alloy plate with a thickness of 1 mm was cut into 15 mm×80 mm rectangular sheets, which were then polished in a polishing machine, and cleaned with water-free ethanol, and then immersed in a 2 wt % NaOH aqueous solution. After 2 minutes, the rectangular sheets were washed with water and dried to obtain pretreated aluminum alloy sheets.

2. Surface Treatment 1:

Each aluminum alloy sheet as an anode was placed in an anodizing bath containing a 20 wt % H₂SO₄ solution, the aluminum alloy sheet was electrolyzed at a voltage of 15V for 5 minutes, and then was blow-dried.

The cross section of the aluminum alloy sheet after the surface treatment 1 was observed by a metalloscope, showing that an aluminum oxide layer with a thickness of 5 μm was formed on the surface of the electrolyzed aluminum alloy sheet. The surface of the aluminum alloy sheet after the surface treatment 1 was observed by an electron microscope (see FIG. 2), showing that nanopores with an average diameter of about 20 nm to about 40 nm and a depth of 3 μm were formed in the aluminum oxide layer.

3. Surface Treatment 2

100 ml aqueous solution containing 5 g NaH₂PO₄ and 1 g NaOH with pH=11.8 was prepared in a beaker. The aluminum alloy sheet after surface treatment 1 was immersed in the sodium carbonate solution, taken out after 3 minutes, placed in a beaker containing water, immersed for 1 minute. The process was repeated for 5 times. After water immersing for the last time, the aluminum alloy sheet was blow-dried.

The surface of the aluminum alloy sheet after the surface treatment 2 was observed by an electron microscope (see FIGS. 3a and 3b ), showing that corrosion pores with an average diameter of 600 nm to 1000 nm and a depth of 2 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores.

4. Molding:

The dried aluminum alloy piece was inserted into an injection mold. A resin composition containing a polyphenylene sulfide (PPS) resin and 30 wt % fiberglass was injection molded. The aluminum alloy resin composite was obtained after being demolded and cooled, including a firm bonding between the aluminum alloy and the resin.

Example 2

In this example, an aluminum alloy resin composite was prepared by a method which was substantially the same as the method in Example 1, with the following exceptions.

The buffer solution used in the surface treatment 2 was a 100 ml aqueous solution containing 10 g NaH₂PO₄ and 1 g NaOH with pH=12.1. It was observed that a layer of aluminum oxide film having a thickness of about 5 μm was formed after electrolysis, and nanopores having diameters of 20-40 nm and depths of 3 μm were formed in the aluminum oxide layer. And it was observed that after surface treatment 2, corrosion pores with diameters of 800-1200 nm and depths of 2 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores. And an aluminum alloy resin composite was prepared.

Example 3

In this example, an aluminum alloy resin composite was prepared by a method which is substantially the same as the method in Example 1, with the following exceptions.

The buffer solution used in the surface treatment 2 is a 100 ml aqueous solution containing 8 g NaH₂PO₄ and 2 g NaOH with pH=12.5. It was observed that a layer of aluminum oxide film having a thickness of about 5 μm was formed after electrolysis, and nanopores having diameters of 20-40 nm and depths of 2 μm were formed in the aluminum oxide layer. And it was observed that after surface treatment 2, corrosion pores with diameters of 800-1600 nm and depths of 3 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores. And an aluminum alloy resin composite was prepared.

Example 4

In this example, an aluminum alloy resin composite was prepared by a method which is substantially the same as the method in Example 1, with the following exceptions.

The buffer solution used in the surface treatment 2 is a 100 ml aqueous solution containing 8 g NaH₂PO₄ and 3 g NaOH with pH=12.9. It was observed that a layer of aluminum oxide film having a thickness of about 5 μm was formed after electrolysis, and nanopores having diameters of 20-40 nm and depths of 0.5 μm were formed in the aluminum oxide layer. And it was observed that after surface treatment 2, corrosion pores with diameters of 1000-2000 nm and depths of 4.5 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores. And an aluminum alloy resin composite was prepared.

Example 5

In this example, an aluminum alloy resin composite was prepared by a method which is substantially the same as the method in Example 1, with the following exceptions.

The buffer solution used in the surface treatment 2 is a 100 ml aqueous solution containing 1 g NaH₂PO₄ and 1 g NaOH with pH=10.5. It was observed that a layer of aluminum oxide film having a thickness of about 5 μm was formed after electrolysis, and nanopores having diameters of 20-40 nm and depths of 4.5 μm were formed in the aluminum oxide layer. And it was observed that after surface treatment 2, corrosion pores with diameters of 300-600 nm and depths of 0.5 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores. And an aluminum alloy resin composite was prepared.

Example 6

In this example, an aluminum alloy resin composite was prepared by a method which was substantially the same as the method in Example 1, with the following exceptions.

The buffer solution used in the surface treatment 2 was a 100 ml aqueous solution containing 5 g KH₂PO₄ and 2 g KOH with pH=12.0. It was observed that a layer of aluminum oxide film having a thickness of about 5 μm was formed after electrolysis, and nanopores having diameters of 20-40 nm and depths of 2 μm were formed in the aluminum oxide layer. And it was observed that after surface treatment 2, corrosion pores with diameters of 600-1000 nm and depths of 3 μm were formed on the surface of the immersed aluminum alloy sheet. It may also be observed that there was a double-layer three-dimensional pore structure in the aluminum oxide layer similar to the structure shown in FIG. 1, and the corrosion pores were communicated with the nanopores. And an aluminum alloy resin composite was prepared.

Comparative Example 1

1. Pretreatment:

A commercially available A5052 aluminum alloy plate with a thickness of 1 mm was cut into 15 mm×80 mm rectangular sheets, which were then polished in a polishing machine, cleaned with water-free ethanol, and then immersed in a 2 wt % NaOH aqueous solution. After 2 minutes, the rectangular sheets were washed with water and dried to obtain pretreated aluminum alloy sheets.

2. Surface-Treatment:

Each aluminum alloy sheet was immersed into a hydrazine hydrate aqueous solution having a concentration of 5 wt % with pH=11.2. After 2 minutes at 50° C., the aluminum alloy sheet was taken out and washed with deionized water. The process was repeated for 30 times. The aluminum alloy sheet was taken out and dried in a drying oven at 60° C.

3. Molding:

The dried aluminum alloy piece was inserted into an injection mold. A resin composition containing a polyphenylene sulfide (PPS) resin and 30 wt % fiberglass was injection molded. The aluminum alloy resin composite was obtained after being demolded and cooled, including a bonding between the aluminum alloy and the resin.

Comparative Example 2

1. Pretreatment:

A commercially available A5052 aluminum alloy plate with a thickness of 1 mm was cut into 15 mm×80 mm rectangular sheets, which were then polished in a polishing machine, and cleaned with water-free ethanol, and then immersed in a 2 wt % NaOH aqueous solution. After 2 minutes, the rectangular sheets were washed with water and dried to obtain pretreated aluminum alloy sheets.

2. Surface-Treatment:

Each aluminum alloy sheet as an anode was placed in an anodizing bath containing a 20 wt % H₂SO₄ solution, the aluminum alloy was electrolyzed at a voltage of 15V for 5 min, and then the aluminum alloy sheet was blow-dried.

3. Molding:

The dried aluminum alloy piece was inserted into an injection mold. A resin composition containing a polyphenylene sulfide (PPS) resin and 30 wt % fiberglass was injection molded. The aluminum alloy resin composite was obtained after being demolded and cooled, including a bonding between the aluminum alloy and the resin.

Performance Test

The connectivity of the aluminum alloy and the resin: the aluminum alloy-resin composites prepared in Examples 1-6 and Comparative examples 1-2 were fixed in a universal material testing machine to perform tensile tests. The test results under maximum load can be regarded as the connectivity force value between the aluminum alloy and the resin. The test results are summarized in Table 1 below.

TABLE 1 Depth of Diameter Diameter Nano- of Nano- Depth of of Connec- pores/ pores/ Corrosion Corrosion tivity μm nm pores/μm pores/nm Force/N Example 1 3 20-40 2 600-1000 1256 Example 2 3 20-40 2 800-1200 1277 Example 3 2 20-40 3 800-1600 1312 Example 4 0.5 20-40 4.5 1000-2000  1189 Example 5 4.5 20-40 0.5 300-600  1228 Example 6 2 20-40 3 600-1000 1232 Comparative  20-100 357 example 1 Comparative 40-60 65 example 2

It can be seen from Table 1 that the bonding between the resin and the aluminum alloy in the aluminum alloy resin composite of the present disclosure can achieve up to 1312N. However, the bonding between the resin and the aluminum alloy in existing aluminum alloy resin composite is only tens or hundreds of newton. The performance of the aluminum alloy resin composite in the present disclosure has been improved significantly, compared with the existing ones. The resin molding process is easier. The aluminum alloy in the present disclosure does not need additional bonding to be combined with the resin. The process of the present disclosure has little effect on the size of the metal substrate and the appearance of the aluminum alloy. At the same time, it is easier to inject mold resin directly into the corrosion holes with a bigger surface. It also has no specific requirement for the synthetic resin. The processes and composites of the present disclosure allow more applications, reduce environmental pollution, and are suitable for mass production.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments cannot be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present disclosure. 

What is claimed is:
 1. A method of preparing an aluminum alloy-resin composite, comprising: S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, the oxide layer including nanopores; S2: immersing the resulting aluminum alloy substrate obtained at step S1 in a buffer solution having a pH of about 10 to about 13, to form corrosion pores on an outer surface of the oxide layer and form a double-layer pore structure including the corrosion pores and the nanopores, wherein the corrosion pores have a larger diameter than the nanopores, the corrosion pores have an average diameter of about 200 nm to about 2000 nm, and the corrosion pores are in communication with the nanopores; and S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained in step S2 in a mold to obtain the aluminum alloy-resin composite.
 2. The method according to claim 1, wherein step S2 comprises repeatedly immersing the resulting aluminum alloy obtained in step S1 in a buffer solution having a pH of about 10 to about 13 for more than one times, wherein each immersing lasts for about 1 min to about 60 minutes, and cleaning the aluminum alloy with water after each immersing.
 3. The method according to claim 2, wherein step S2 comprises repeatedly immersing the resulting aluminum alloy in step S1 in a buffer solution having a pH of about 10 to about 13 for about 2-10 times.
 4. The method according to claim 1, wherein the nanopores have an average diameter of about 10 to about 100 nm; the corrosion pores have an average diameter of about 200 nm to about 2000 nm; and the oxide layer has a thickness of about 1 μm to about 5 μm.
 5. The method according to claim 1, wherein anodizing the surface of the aluminum alloy substrate comprises: providing the aluminum alloy substrate as an anode in a H₂SO₄ solution with a concentration of about 10 wt % to about 30 wt %; and electrolyzing the aluminum alloy substrate at a temperature of about 10° C. to about 30° C. at a voltage of about 10V to about 20V for about 1 min to about 40 min to form the oxide layer with a thickness of about 1 μm to about 10 μm on the surface of the aluminum alloy substrate.
 6. The method according to claim 1, further comprising applying a pretreatment to the aluminum alloy substrate, wherein, the pretreatment includes: oil removal, a first washing with water, alkali etching, a second washing with water, neutralizing, and a third washing with water.
 7. The method according to claim 1, wherein the resin is a thermoplastic resin.
 8. A method of preparing an aluminum alloy-resin composite, comprising: S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, the oxide layer including nanopores; S2: immersing the resulting aluminum alloy substrate obtained at step S1 in a buffer solution having a pH of about 10 to about 13, to form corrosion pores on an outer surface of the oxide layer and form a double-layer pore structure including the corrosion pores and the nanopores, the corrosion pores being wherein the corrosion pores have a larger diameter than the nanopores; and S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained in step S2 in a mold to obtain the aluminum alloy-resin composite, wherein the buffer solution comprises a soluble alkali and a soluble dihydrogen phosphate.
 9. The method according to claim 8, wherein the dihydrogen phosphate includes at least one selected from a group of sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, and aluminum dihydrogen phosphate; the soluble alkali includes at least one selected from a group of sodium hydroxide and potassium hydroxide.
 10. The method according to claim 9, wherein, in the buffer solution, the dihydrogen phosphate has a concentration of about 50 wt % to about 99 wt %, and the soluble alkali has a concentration of about 1 wt % to about 50 wt %.
 11. The method according to claim 10, wherein, in the buffer solution, the dihydrogen phosphate has a concentration of about 60 wt % to about 99 wt %, and the soluble alkali has a concentration of about 1 wt % to about 40 wt %.
 12. A method of preparing an aluminum alloy-resin composite, comprising: S1: anodizing a surface of an aluminum alloy substrate to form an oxide layer on the surface, the oxide layer including nanopores; S2: immersing the resulting aluminum alloy substrate obtained at step S1 in a buffer solution having a pH of about 10 to about 13, to form corrosion pores on an outer surface of the oxide layer and form a double-layer pore structure including the corrosion pores and the nanopores, the corrosion pores being in communication with the nanopores, wherein the corrosion pores have an average diameter of about 200 nm and the corrosion pores have a larger diameter than the nanopores; and S3: injection molding a resin onto the surface of the resulting aluminum alloy substrate obtained in step S2 in a mold to obtain the aluminum alloy-resin composite, wherein the resin is a thermoplastic resin, and wherein the thermoplastic resin includes a main resin and a polyolefin resin.
 13. The method according to claim 12, wherein the main resin includes polyphenylene ether and polyphenylene sulfide, and the polyolefin resin has a melting point of about 65° C. to about 105° C.
 14. The method according to claim 13, wherein in the main resin, the weight ratio of polyphenylene ether to polyphenylene sulfide is about 3:1 to about 1:3.
 15. The method according to claim 12, wherein the main resin includes polyphenylene oxide and polyamide, and the polyolefin resin has a melting point of about 65° C. to about 105° C.
 16. The method according to claim 15, wherein in the main resin, the weight ratio of polyphenylene oxide to polyamide is about 3:1 to about 1:3.
 17. The method according to claim 12, wherein the main resin includes polycarbonate, and the polyolefin resin has a melting point of about 65° C. to about 105° C.
 18. The method according to claim 12, wherein based on 100 weight parts of the thermoplastic resin, the amount of the main resin is about 70 weight parts to about 95 weight parts, and the amount of the polyolefin resin is about 5 weight parts to about 30 weight parts.
 19. The method according to claim 12, wherein based on 100 weight parts of the thermoplastic resin, the thermoplastic resin includes a flow improver with about 1 weight part to about 5 weight parts; and wherein the flow improver includes a cyclic polyester. 